1. Field of the Invention
The present invention relates to an apparatus and a method for observing a sample submerged in a liquid by using a scanning probe microscope.
2. Description of the Related Art
The scanning probe microscope is a device whereby the surface of a sample can be observed with high resolution, and includes an interatomic force microscope (AFM) and a scanning tunneling microscope (STM).
In the interatomic force microscope, a cantilever having a probe arranged at the forward end thereof is brought in closely opposed relation to the surface of a sample and the sample surface is scanned by the probe thereby to measure the displacement of the cantilever caused by the interatomic force exerted between the probe and the sample. The amount of displacement is proportional to the interatomic force exerted between the probe and the sample surface. Therefore, the shape of the sample surface can be measured, by scanning the probe relatively on the sample surface while detecting and maintaining a constant amount of displacement by feedback.
With the scanning tunneling microscope, on the other hand, a bias voltage is applied between a probe and a sample, and a tunnel current flowing between the probe and the sample is measured. The probe is scanned on the sample surface while maintaining a constant tunnel current by feedback, for example. Since the probe moves along the shape of the sample surface, the surface shape of the sample can be measured.
A sample submerged in a liquid may be observed under the scanning probe microscope. FIG. 1 shows a type of interatomic force microscope for observing a sample submerged in a liquid.
In FIG. 1, reference numeral 1 designates a light source for emitting light such as a laser beam, numeral 2 a cantilever having a probe 3 at the forward end thereof for reflecting the light emitted from the light source 1 and refracted in a prism 4, and numeral 5 a light detector such as a photodiode for detecting the light reflected on the cantilever and further on a mirror 6. Numeral 8 designates a sample fully submerged in a liquid 9 contained in a cup-shaped container 10 having an open upper portion. The cantilever 2 is mounted with the probe 3 directed down on a support member 7 fixed on a fixing portion, not shown, in such a manner as to be submerged in the liquid 9 filling the container 10. A piezoelectric actuator 11 is mounted on the lower surface of the bottom of the container 10. As a result, the sample 8 can be moved together with the container 10 in any of x, y and z directions.
In the interatomic force microscope, the z-axis piezoelectric device of the piezoelectric actuator 11 is driven by a z-axis (vertical axis in FIG. 1) height adjust signal from a scan generator (not shown), so that the distance between the probe 3 and the sample 8 is set to an initial distance d (nm). The light emitted from the light source 1, on the other hand, is refracted in the prism 4 and reflected on the surface of the side of the cantilever 2 far from the sample. The reflected light is reflected on the mirror 6 and detected by the light detector 5. Under this condition, the x-axis and y-axis piezoelectric devices of the piezoelectric actuator 11 are driven by a control signal produced from the scan generator, so that the sample 8 is moved along the x-axis direction (lateral direction in FIG. 1) and the y-axis direction (longitudinal direction perpendicular to the x axis in FIG. 1), respectively. Due to unevenness on the surface of the sample 8 to be observed, the distance between the probe 3 and the surface to be observed deviates from the initial distance d, thereby changing the interatomic force between the probe 3 and the sample 8. In this case, the probe 3, trying to maintain the initial distance d, is moved vertically in accordance with the unevennesses of the surface to be observed. This vertical movement also changes the inclination of the cantilever 2, and hence the position of the reflected light entering the light detector 5. The detected position change of the reflected light is converted to the position change in z-axis direction, and based on the converted signal (image signal), an image of an uneven surface of the sample in the liquid is observed.
Also when observing a sample submerged in a liquid under the scanning tunneling microscope, as in the case of the interatomic force microscope described above, a sample is submerged in a liquid filling a cup-shaped container and brought close to the probe, so that a measurement is taken while applying a bias voltage between the probe and the sample.
The use of the scanning probe microscope makes it possible to observe the surface change of a sample in the electrochemical reaction process in an electrolytic solution and thus observe the chemical reaction visually. In such a case, the sample is submerged in the electrolytic solution and the probe is brought close to the sample to obtain a surface image of the sample. However, since the upper portion of the sample container is open, the electrolytic solution is volatilized and the composition of the electrolytic solution changes during the observation, thereby making a correct analysis of the chemical reaction impossible. On the other hand, in the case of the scanning tunneling microscope, the Faraday current flows from the probe in addition to the tunnel current. Therefore, the tunnel current cannot be accurately measured and an STM image cannot be obtained. Further, when the cantilever scans the surface of the sample, fluctuation of the liquid surface occurs and disturbs the optical axis of the laser beam, thereby making it impossible to produce a stable image.
The object of the present invention is to provide an apparatus and method for observing a submerged sample using the scanning probe microscope, wherein the adverse effects of a change in the concentration and composition of the liquid due to the volatilization of the liquid, generation of a leak current in the probe and fluctuation of the liquid surface are eliminated to produce a stable surface image.
In order to solve these problems, according to one aspect of the invention, there is provided a submerged sample observation apparatus comprising:
a scanning probe microscope including a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever;
a sample container having a side wall for holding a liquid therein; and
means arranged on the surface of the liquid for preventing volatilization of the liquid;
wherein the probe is brought in closely opposed relation to a sample in the liquid in the sample container, the relative positions of a probe and a sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample.
According to another aspect of the invention, there is provided a submerged sample observation apparatus comprising:
a scanning probe microscope including a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever; and
a sample container having a side wall for holding a liquid therein;
wherein the probe is brought in closely opposed relation to a sample in the liquid in the sample container, the relative positions of a probe and a sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample, and
wherein an insulative liquid layer not mixed with the liquid having the sample submerged therein is formed on the surface of the liquid, and only the forward end portion of the probe is introduced into the liquid having the sample submerged therein, while the remaining portion of the probe is covered by the insulative liquid layer.
According to still another aspect of the invention, there is provided a submerged sample observation apparatus comprising:
a scanning probe microscope including a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever; and
a sample container having a side wall for holding a liquid therein;
wherein the probe is brought in closely opposed relation to a sample in the liquid in the sample container, the relative positions of a probe and a sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample, and
wherein the light from the light source is applied to the cantilever in the liquid without passing through the interface between the atmosphere and the liquid having the sample submerged therein, and the reflected light is picked up in the liquid.
According to yet another aspect of the invention, there is provided a method of observing a sample submerged in a liquid using a scanning probe microscope comprising a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever;
wherein the probe is brought in closely opposed relation to a sample in the liquid in a sample container, the relative positions of the probe and the sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample, and
wherein means for preventing the volatilization of the liquid is arranged on the surface of the liquid.
According to a further aspect of the invention, there is provided a method of observing a sample submerged in a liquid using a scanning probe microscope comprising a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever;
wherein the probe is brought in closely opposed relation to the sample in the liquid in the sample container, the relative positions of the probe and the sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample, and
wherein an insulative liquid layer not mixed with the liquid having the sample submerged therein is formed on the liquid, and only the forward end portion of the probe is placed in the liquid while the remaining portion of the probe is covered by the insulative liquid layer.
According to a still further aspect of the invention, there is provided a method of observing a sample submerged in a liquid using a scanning probe microscope comprising a cantilever having a probe arranged at the forward end thereof, a light source for applying light on the cantilever and a detector for detecting the light reflected from the cantilever;
wherein the probe is brought into closely opposed relation to the sample in the liquid in a sample container, the relative positions of the probe and the sample are changed and, based on the interaction between the probe and the sample, a surface image of the sample is produced thereby to observe the sample, and
wherein the light from the light source is applied to the cantilever in the liquid without passing through the interface between the atmosphere and the liquid having the sample submerged therein, and the reflected light is picked up in the liquid.
According to this invention, the means for preventing volatilization of the liquid having the sample submerged therein is provided on the surface of the surface of the particular liquid, and therefore volatilization of the liquid during the observation of the sample is prevented, and the chemical reaction can be observed in stable fashion. Also, in view of the fact that only the forward end of the probe is placed in the liquid having the sample submerged therein while the remaining portion of the probe is covered with the insulative liquid layer, therefore generation of Faraday current is suppressed in the probe, and the tunnel current can be accurately measured. Further, the light from the light source and the reflected light do not pass through the interface between the atmosphere and the liquid having the sample submerged therein, so that even when the surface of the liquid fluctuates, the effect of the fluctuation can be avoided.